Tie2 is an endothelial receptor tyrosine kinase (RTK) that is required for physiological and pathological angiogenesis. The ligands for Tie2, the Angiopoietins, have context-dependent effects on angiogenesis and vascular maintenance. Recent evidence suggests that metalloprotease-mediated shedding of a soluble Tie2 {sTie2) protein regulates the Tie2/Ang system, although the mechanisms of its production and function are not known. In humans, sTie2 is detectable in the serum of healthy control subjects, and it is increased in disease states associated with vascular regression, such as congestive heart failure and hypertension, suggesting a potential anti-angiogenic function for sTie2. Consistent with these findings, overexpression of an engineered soluble Tie2 protein blocks both physiological and pathological angiogenesis in preclinical models. sTie2 shedding from endothelial cells is induced by VEGF and is dependent on the phosphoinositide (PI) 3-kinase/Akt pathway. Furthermore, plasma concentrations of sTie2 and VEGF are significantly increased in patients with the most severe manifestation of peripheral arterial disease (PAD). These findings suggest that sTie2 modulates the angiogenic response. The effector protease responsible for Tie2 cleavage has not previously been identified, although the primary candidate mediators of sTie2 shedding are the ADAM (a disintegrin and metalloprotease) proteins. ADAM15 has been shown to be required for pathological angiogenesis, and preliminary studies in this proposal will demonstrate that ADAM15 is required for sTie2 shedding from endothelial cells. To date, the role of elevated sTie2 in CLI and other disease states is not known, and whether ADAM15 is involved in sTie2 shedding in vivo remains unclear. In this proposal, we hypothesize that ADAM15 is the principal protease for Tie2 cleavage in endothelial cells and that ADAM15-induced sTie2 is required for ischemic angiogenesis. To test this hypothesis, the Specific Aims of this proposal are to: 1) Identify the role of ADAM15 in sTie2 shedding and the molecular mechanism of ADAM15 activation;and 2) Determine the requirement for ADAM 15 in ischemic angiogenesis in vivo. Accomplishing these Specific Aims will provide key insights into the mechanisms regulating sTie2 shedding as well as its role in ischemic angiogenesis such as in PAD.